Recovering Kodaira types from $\ell$-torsion on elliptic curves
Abstract
The classical N\'eron-Ogg-Shafarevich criterion characterises good reduction of an elliptic curve over a -adic field via the action of inertia on the -adic Tate module. However, the action of inertia on is not sufficient to distinguish between potentially good and multiplicative reduction, and the action on is not sufficient to determine the Kodaira type. We remedy this situation by endowing with a distance function that records the -adic distances between the -coordinates of the points. We show that, equipped with this additional structure, determines the Kodaira type of the elliptic curve. In the case of residue characteristic , we assume that does not have potentially good reduction of type .
Keywords
Cite
@article{arxiv.2607.02678,
title = {Recovering Kodaira types from $\ell$-torsion on elliptic curves},
author = {Naina Praveen},
journal= {arXiv preprint arXiv:2607.02678},
year = {2026}
}
Comments
11 pages. First version. Comments welcome!